WASHINGTON — Marine Lt. Col. Oliver L. North, the National Security Council official accused of funneling Iranian arms sales profits to the Nicaraguan rebels, last weekend destroyed a series of documents from NSC files that are believed to have indicated the scope of involvement in the venture by other Administration officials, government sources said Wednesday.

Destruction of the potentially crucial documents is now being investigated by the FBI, which did not enter the case until Wednesday, one senior government source said.

Although the contents of the documents in question could not be determined precisely, sources said they could have played an important role in the Administration's effort to establish the full dimensions of the mushrooming scandal--especially the question of how many officials were involved.

North, who was relieved of his duties by President Reagan on Tuesday, entered his secure office adjacent to the White House and shredded the papers at least 36 hours before Administration officials dispatched White House security officers to change the combinations on North's office and safe locks Tuesday afternoon, government sources said.

It was not clear whether North acted before or after being interviewed last weekend by Atty. Gen Edwin Meese III and other senior Justice Department officials about his role in the affair, the sources said.

However, because Meese conducted the first stage of the Iran probe personally, without drawing on the FBI's expertise, the sources indicated, North's office was left unguarded during a critical period when he was under scrutiny for his role in the Iran arms-and-hostages deal.

'Closed the Barn Door'

"Too late," one knowledgeable source said. "He was shredding over the weekend. They closed the barn door after the horses were gone."

The allegations further complicate what has become the most serious crisis of President Reagan's six years in office, and they could lead to criminal charges, legal experts said.

Meanwhile, there were these further developments Wednesday:

--The Justice Department's investigation of the scandal focused on whether Administration officials other than those who have already left office were involved in the diversion of profits from Iranian arms sales to the U.S.-backed rebels, known as contras, in Nicaragua.

In addition to removing North, Reagan on Tuesday accepted the resignation of his national security adviser, Vice Adm. John M. Poindexter. Meese said that Poindexter, who was North's boss, knew--but did not tell the President--that profits from sales of arms to Iran were being diverted at a time when Congress had banned U.S. military aid to the contras.

--Meese, who is heading the investigation, said that evidence gathered so far has "pretty clearly established" that Reagan and his top assistants who remain in office were not involved. However, Meese and other officials close to the investigation said he was speaking only on the basis of preliminary interviews.

A comprehensive inquiry is just getting under way. As of Wednesday, sources said, a number of officials across the government believed to have knowledge of the Iran arms operation and North's activities had not been interviewed or contacted by investigators.

--Reagan appointed a three-man commission, headed by former Sen. John Tower (R-Tex.), to review the Administration's foreign policy-making apparatus, especially the role of the President's national security adviser and his staff. The commission is expected to produce general policy-making and organizational recommendations, not a detailed account of the present controversy.

The other commission members are former Sen. Edmund S. Muskie (D-Maine), who served as secretary of state in the Jimmy Carter Administration, and Brent Scowcroft, who served as national security adviser in the Gerald R. Ford Administration.

Reagan on Wednesday personally telephoned North to offer his thanks for his service in his National Security Council post, an associate said. But North was described as depressed and extremely angry over his dismissal after initially accepting the news with equanimity.

North was said to be especially concerned about support for his family and about continuing uncertainty over his future--if any--in the Marine Corps. He reportedly told friends that he did nothing wrong and only followed orders.

But Defense Secretary Caspar W. Weinberger was reported by one source Wednesday to be reluctant to see North return to Marine duty. Administration officials apparently have reached no decision on where, if anywhere, North will be dispatched now that he has been fired from the NSC.